HEAT TREATMENT APPARATUS FOR TURBINE BLADES

Abstract: Heating apparatus adapted for the heat treatment of turbine blades comprising a support member formed with a plurality of slots. Heating elements in the form of electrically conductive wires surrounded by ceramic insulators are attached to the support member by a pin passing through the ceramic insulator through the support member, so that the heating elments are connected to the support member but are capable of movement relative thereto along the line of the slot. In use of the apparatus, the heating apparatus can be secured to a blade to be heat treated and while in secured position, the heating elements may still be moved to access a work area or to enable the re-distribution of heat to ensure that particular areas of the blade are heated to the required temperature.

Description: Title: "Heat treatment apparatus for turbine blades" The present invention relates to apparatus for the heat treatment of turbine blades. Heat treatment of turbine blades is necessary for stress relief after repair of the blades, which repair step may involve the input of considerable heat such as occurs during welding or brazing and furthermore it has been found that in some cases where, for example, welding operations are carried out, heat treatment of the blade both prior to the welding operation and during the welding operation can also be advantageous in minimising stress and/or distortion that may occur to the blade during a welding operation. British patent specification No. 2,144,361 discloses the attachment of electrically heated elements often referred to as heating mats to a turbine blade by means of wires which are used to secure the mats in position. British patent application No. 9113755.4 discloses a glove type heater comprising two parts which may be pivotally connected together, the two parts carrying heating elements and being providing with slots to enable the glove to be slid over the turbine blade from an outer end, the slots accommodating protrusions such as snubbers. The heater glove permits of a rapid and secure installation of heating elements to the turbine blade to enable stress relieving heat treatment to take place. It has been found that in some cases, particularly with large free standing turbine blades, i.e. those not tied together by lacing wires, snubbers or the like, a change in the mass of metal per unit length between the tip of the blade and the area of the blade adjacent the root part is so great that a heater glove of the type shown in British application 9113755.4 may not always be entirely suitable. It has also been found that for successful heat treatment to relieve stress in a repaired blade the temperatures to which various parts of the blade have to be heated and the length of time for which they are held at such temperatures can be very critical and the difference of just a few degrees from a desired temperature may be detrimental to successful stress relief. It is an object of the present invention to provide a new or improved apparatus for the heat treatment of turbine blades. According to one aspect of the present invention we provide heating apparatus adapted for the heat treatment of turbine blades, said heating apparatus comprising: (a) a support member; (b) a plurality of heating elements; (c) connection means connecting the heating elements to said support member; (d) said connection means permitting of positional adjustment of said heating elements relative to said support member. Preferably the or each support member comprises a substantially planar member and, for example, may comprise a piece of relatively resilient steel which is capable of being resiliently deformed to a required shape without the application of any great force. Conveniently said support member is provided with a variety of slots, said heating elements may be provided with a plurality of holes and connection means in the form of pin-like members may be provided, the arrangement being such that each said pin-like member passes through a respective slot in the support member, and through a hole in one of the heating elements, whereby the heating element may be moved relative to said support member whilst in a secured position by sliding the heating element and connection means relative to the support member in a direction longitudinally aligned with said slot. Said connection means may comprise a pin similar to a cotter pin and washers may be provided at either end, one to prevent the head passing through the slot and at the other end a washer may be provided and the ends of the cotter pin bent over so as to prevent separation of the heating elements from the support means. The relative adjustment provided by the support member and the heating elements enables different heating elements to be provided on different parts of the support member, it enables movement of one heating element relative to another perhaps to provide a gap to permit of access to a work area and in many cases it may be only necessary to have a single support member, heating means constituted by the heating elements collectively extending beyond a lateral edge of the support member whereby it may be folded over, assuming it is of the flexible type, to cover the other side of the turbine blade remote from that on which the heating means and support member is placed. The support member may be located on one side of the turbine blade by any convenient means and may itself be provided with attachment means whereby it may be attached to the blade. The attachment means may comprise a length of wire or other material that will not be adversely affected by the heat, a piece of wire passing around the heating means and if the blade is not surrounded by heating means, a surface of the blade, the two ends of the wire being twisted together to hold the heating apparatus in position. Alternatively, wires may be attached to the blade in a manner as described in British patent specification no. 2144361 to secure the heating apparatus to the blade. Alternatively, clips may be provided that have a surface engaging with the heating apparatus and a surface that engages with another heating apparatus or with a blade in a manner similar to that shown in British patent application no. 9113755.4. The support member, plus the addition of a plurality of heating elements permits of many different combinations of heat input so as to enable different size and thicknesses of blades to be properly heated and whereby various parts of the blade can receive an adequate amount of heat and hence a proper heat treatment irrespective of the variation in thickness imparts to the blade. The provision of a support member only on one side of the blade not only satisfactorily holds and locates the heating means in the desired position but where the heating means extends laterally beyond an edge of the blade enables heat treatment on both sides of the blade whilst, if desired, by modifying the shape of one or more heating means, allowing access for a repair operation to be carried out on the blade. The present invention will now be described by way of example only with reference to the accompanying drawings, wherein: FIGURE 1 illustrates one embodiment of support member; FIGURE 2 is an illustration of part of a heating means; FIGURE 3 is a cross-sectional view of the heating means attached to the support member; FIGURE 4 is an illustration of a turbine blade on which the heating means has been positioned. Referring to Figure 1, one embodiment of support member is shown and comprises a substantially planar member 10 which may for example be a piece of resilient steel approximately 1mm thickness and is formed with a series of slots 11 and holes 12. The planar member 10 will have a certain amount of natural resilience so that it may be bent to conform approximately to fairly complex shapes that are found in turbine blades including concave and convex surfaces, the radii of which change along the length of the blade. Figure 2 shows a typical heating means which comprises a plurality of ceramic elements 15, 16 for example, the ceramic elements being pivotally connected by connecting means 17, 18, 19 to adjacent ceramic heating means 20 and 21, the ceramic elements 15, 16, 20 and 21 have electrically conductive heating wires passing therethrough, the wires passing through the pivotal connection means 17, 18 through which a current may be passed via a supply to terminals 22 and 23. The pivotal connections provide a mat which may be easily folded to conform to the complex shapes of turbine blades. The mats, such as the mat shown in Figure 2, are secured to the support member 10, for example by passing a cotter pin, such as the cotter pin shown at 25, through a slot such as the slot 11 in the support member 10 and through a hole, such as the hole 26 in the ceramic member 15. A washer 27 can be placed at the headed end 28 of the cotter pin 25 and once the pin has been passed through the support member 10 and the ceramic member 15 the ends 30 and 31 can be bent over after a washer 32 has been placed over the ends. Thus the heating mat is secured firmly to the support member 10 but may be moved relative thereto along the direction of the slots by an amount equal to the length of the slots 11 which of course may be made of any desired length. In addition to the adjustment along the length of the support member 10 the heating mat may be fixed so that it extends only partially across the support member 10, fully across or may have a length whereby it considerably exceeds the width of the support member 10 thereby allowing the heating mat to be doubled over to provide additional heat on one side or possibly after the support member and heating mat has been brought into abutment with a turbine blade, folded over the blade to provide heat on the other side of the blade. Referring now to Figure 4, a sketch of a heating apparatus in accordance with the present invention is shown around a turbine blade 35. The turbine blade 35 has secured thereto the support member 10 which carries a plurality of different heating mats such as the part of the heating mat shown in Figure 2 and it can be seen that along the length shown by arrow A, the heating mats are only on one side of the blade and not of a length so that they can be folded over the blade. Along the length B the heating mat is of a length whereby it can be folded right across the blade and that both sides of the blade will be provided with approximately equal heat. Along the length C there is no heating mat at all, this might be the case where it is actually desired to work with a welding apparatus, for example in the area C. Along the length D the heating mats cover the underside of the blade fully but only partially cover the upper surface leaving a part free from any heating means. The end length E is fully covered with a heating mat. It will be appreciated that the illustration of Figure 4 is merely an example showing the variations that may be provided by the support means and heating mats of the present invention in combination and which allow an almost universal variation in the heating means applied to the blade and hence the heat input to various parts of the blade so that the blade 35 as a whole may be subjected to a correct heat treatment whereby the various areas of the blade can be heated to a proper temperature and maintained at that temperature for desired lengths of time without variation of temperatures from a predetermined fairly narrow band. It will be appreciated that whereas in the embodiment shown the support member has been secured to the underside or concave side of the blade, it may equally well be applied to the convex side of the blade and it is also envisaged that the heating mats may be of a length whereby they can be folded over to cover the whole of the blade but in the first preheat operation they may be left in a position whereby they heat one side of the blade only, the other half of the matter being allowed to hang away from the blade and this may continue during a welding operation on the blade and in a subsequent heat treatment operation some or all of the hanging ends of the mats may be brought into contact with the blade to effect proper heat treatment. It is also envisaged that the support member may be provided with many different heating mats of different shapes and thicknesses and different heat outputs so as to provide for a large range of different heat outputs depending on the thickness and mass of metal of the blade at various positions along its length. The features disclosed in the foregoing description, or the accompanying drawings, expressed in their specific forms or in the terms of means for performing the desired function, or a method or process for attaining the disclosed result, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS 1. Heating apparatus adapted for the heat treatment of turbine blades, said heating apparatus comprising: (a) a support member; (b) a plurality of heating elements; (c) connection means connecting the heating elements to said support member; (d) said connection means permitting of positional adjustment of said heating elements relative to said support member. 2. Heating apparatus as claimed in Claim 1 wherein the support member comprises a substantially planar member and is of a resilient material. 3. Heating apparatus as claimed in Claim 2 wherein the support member comprises a resilient steel capable of resilient deformation to a required shape without the application of any considerable force. 4. Heating apparatus as claimed in any one of the preceding claims wherein the support member is provided with a plurality of slots and said heating element or parts associated with said heating elements are provided with a plurality of holes and said connection means comprise pin-like members, the arrangement being that a pin-like member passes through a respective slot in the support member and through a hole in one of the heating elements or parts associated therewith enabling the heating element to be moved relative to said support member whilst secured thereto in a direction aligned with said slot. 5. Heating apparatus as claimed in any one of the preceding claims wherein said connection means comprises a cotter-like pin and a pair of washers, one of said washers provided to prevent the head passing through a slot provided in said support member and the other washer being provided adjacent to said heating element or part associated therewith, the ends of said cotter pin being bent over in contact with said second washer, said cotter-like pin thereby maintaining the heating element connected to said support means. 6. Heating apparatus as claimed in Claim 4 or Claim 5 wherein said pin¬ like member is of a length enabling a plurality of heating means to be connected to a respective slot in said support member. 7. Heating apparatus as claimed in any one of the preceding claims wherein said support member is provided with a plurality of slots and a plurality of substantially annular holes. 8. Heating apparatus as claimed in any one of the preceding claims wherein said heating elements each comprise an electrically conductive element surrounded at least partially by insulating means in the form of a ceramic element. 9. Heating apparatus as claimed in any one of the preceding claims further comprising attachment means adapted to attach the heating apparatus to a turbine blade. 10. Heating apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. 11. Heating apparatus including any novel feature or novel combination of features as disclosed herein and/or as illustrated in the accompanying drawings.

Inventors: FRASER MICHAEL JAMES, FRASER, MICHAEL, JAMES
Applicants: FRASER MICHAEL JAMES, TURBINE BLADING LTD, FRASER, MICHAEL, JAMES, TURBINE BLADING LIMITED
Application year: 1994
Main classification: H05B3
IPC codes: F01D5, F02C7, H05B3